The epidemiological pattern of seasonal influenza in four sentinel sites in Iraq

Abstract Introduction Influenza is an acute viral infection with significant morbidity and mortality. It occurs annually each winter, which is called seasonal influenza, and is preventable through safe vaccine. Aim The aim of this work is to know the epidemiological pattern of patients with seasonal influenza in Iraqi sentinel sites. Methods A cross‐sectional study was carried out on records of patients who attended four sentinel sites and registered to have influenza‐like illness (ILI) or severe acute respiratory infection (SARI), and laboratory investigated. Results The total number of cases was 1124; 36.2% of them aged 19–39 years; 53.9% were female; 74.9% lived in urban areas; 64.3% diagnosed as ILI; and 35.7% as SARI; 15.9% had diabetes, 12.7% had heart disease, 4.8% had asthma, 3% had a chronic lung disease, and 2% had hematological disease; 94.6% did not get influenza vaccine. About COVID‐19 vaccine, 69.4% were not vaccinated, 3.5% got only one dose, and 27.1% completed two doses. Only the SARI cases needed admission; among them, 95.7% were cured. 6.5% were diagnosed with influenza‐A virus, 26.1% had COVID‐19, and 67.5% were negative. Among those with influenza, 97.3% had H3N2 subtype and 2.7% had H1N1 pdm09. Conclusions The percentage of influenza virus in Iraq is relatively small. The age, classification of case (ILI or SARI), having diabetes, heart disease, or immunological disease, and taking COVID‐19 vaccine have a significant association with influenza. Recommendations It is needed for similar sentinel sites in other health directorates and for rising health education about seasonal influenza and its vaccine.


| INTRODUCTION
Influenza is an acute viral respiratory infection that causes significant morbidity and mortality worldwide. Three types of influenza virus could cause disease in humans: A, B, and C. Influenza A is the most type responsible for causing pandemics because of its high susceptibility to antigenic variation. 1 Influenza is a common virus whose ability to change its genetic makeup allows for a disease of pandemic proportion. 2 It is a highly contagious and deadly virus, killing nearly half a million people yearly worldwide. The classic symptoms of the disease are fever, fatigue, cough, and body aches. In the outpatient setting, diagnosis can be made by clinical presentation with optional confirmatory diagnostic testing. 3 The outbreak of influenza virus that usually occurs annually each winter is called seasonal influenza. 4 In a majority of cases, seasonal influenza is preventable through safe and readily available vaccinations. 5 The World Health Organization (WHO) estimated that seasonal influenza epidemics could cause three to five million severe cases annually and 290 000 to 650 000 deaths globally. Infection with seasonal influenza is mainly caused by influenza virus type A and type B. 6,7 Pregnant women, young children, the elderly, and persons with chronic illnesses are at high risk for severe illness and death associated with influenza viral infection. Seasonal influenza vaccination is the most effective way to prevent the infection and its complications. 8 The vaccines are almost available but must be regularly updated. 6 Understanding geographical and temporal patterns of seasonal influenza can help strengthen influenza surveillance to early detect epidemics and inform influenza prevention and control programs. 9 Sentinel surveillance is defined as the monitoring of rate of occurrence of specific diseases/conditions through a voluntary network of doctors, laboratories, and public health departments with a view to assess the stability or change in health levels of a population. 10 Data collected in a well-designed sentinel system can be used to signal trends, identify outbreaks, and monitor disease burden, providing a rapid and economical alternative to other surveillance methods. Sentinel systems involve a network of reporting sites, typically doctors, laboratories, and public health departments. 11 Knowledge of the epidemiological pattern among patients with seasonal influenza in Iraqi sentinel surveillance sites could be helpful in (1) early detection and rapid response to influenza outbreaks,

| METHODOLOGY
It is a cross-sectional study design. The four sites of Iraqi sentinel surveillance for seasonal influenza were selected to be the study settings; two are located in Baghdad; the capital (which are Al-Nu'man Teaching Hospital in Rusafa "the eastern side" and Imamain Kadhimain Medical City in Karkh "the western side"), one in Erbil; in the north (Erbil Teaching Hospital), and one in Basra; in the south (Basra Teaching Hospital). The study populations in this work are all Iraqi patients, and all were recorded to have influenza-like illness (ILI) or severe acute respiratory infection (SARI). The sampling was carried out for those cases who did match the inclusion criteria of both categories according to the WHO definition, which were registered in the four mentioned surveillance sites, from Nov. 2021, which is the date of establishing of those sites, till May 2022. There are two sentinel sites responsible for registration of cases with ILI, which are Al-N'uman and Erbil Teaching Hospitals, while the other two sites are responsible for registration of cases with SARI "according to the WHO definition." Regarding the tools of the study, this work involved the epidemiological characteristics of the participants according to their filled out special standard case-investigation forms, which were registered in the mentioned four surveillance hospitals. These characteristics include the following variables: Age, sex, status of pregnancy, address, present and past medical history, classification of case (ILI or SARI), presence of some medical risk factors, status of immunization against influenza and COVID-19, patient admission status and severity, final fate, type of sample, and type of virus and its strain after laboratory analysis at the Central Public Health Laboratory. The gathered data were coded for each participant and analyzed by SPSS 20 program, and then the data were summarized, analyzed, and presented as tables and charts.
Chi-square tests were done for comparison between the variables, and p value of <0.5 was considered in the determination of presence of any significant statistical association between those variables.

| RESULTS
The total number of cases that were registered by the four sentinel surveillance sites for seasonal influenza in Iraq since their establishment in Nov. 2021 till May 2022 was 1124. The distribution of those cases regarding some personal and clinical variables is illustrated in Table 1, while their distribution regarding the presence of health problems is shown in Table 2.
The most common cases were distributed in December and March respectively as shown in Figure 1.
The total number of cases of influenza A virus who attended Iraqi sentinel sites was 73; most cases were distributed at the end of November and the first half of December as shown in Figure 2.
About 95% of all SARI cases were cured, and only 3.74% died; regarding the oxygen needed, about 16% were received as shown in Table 3.
The distribution of personal, demographic, and clinical variables among patients who had influenza virus and those who did not have influenza virus and their association are shown in Table 4.

| DISCUSSION
The total number of patients that were registered in those sites was 1124. Among those patients, about two thirds (64.3%) were enrolled as ILI and about one third (35.7%) were enrolled as SARI, which required admission to a hospital. More than two thirds of all cases (66.5%) were registered in Baghdad, which could reflect the high population density in the Iraqi capital, in which more than 7.5 million are living. 12,13 The largest age groups among the Iraqi patients who